Wastewater treatment is essential for preventing disease and protecting the environment, but current treatment processes are energy intensive and emit greenhouse gas (GHG) due to fossil fuel use and organic degradation. Every year, approximately 12 trillion gallons of municipal wastewater are treated by publicly owned treatment works in the U.S., and this consumes about 15 GW, or 3% of the total electricity produced in the U.S. In the meantime, approximately 0.73×109 ton (Gt) of carbon dioxide-eq/yr emission is attributed to the degradation of organics in wastewater, equivalent to nearly 1.5% of the GHG emissions of 49 Gt carbon dioxide-eq/yr. These numbers are even larger when industrial and agricultural wastewater treatment industries are included. Great progress has been made to increase energy efficiency and recover renewable energy from wastewater using technologies such as anaerobic digestion and bioelectrochemical systems, because the chemical energy content embedded in wastewater is estimated to be multiple times that required to treat the wastewater. However, these methods reduce only fossil fuel consumption and its associated carbon emission.
Point-source carbon dioxide (CO2) mitigation, in particular carbon capture and storage (CCS), has been a main strategy for reducing industrial and energy-related CO2 emissions (e.g., power plants, cement and petrochemical industries, and so forth), which account for approximately 60% total CO2 emission due to fossil-fuel use. Conventional CCS consists of energy-intensive and costly CO2 separation, purification, compression, transportation, and injection underground. A power plant equipped with CCS incurs at least a 10-40% energy penalty primarily due to the high-energy-demand solvent/sorbent regeneration process. Emerging membrane technologies minimize regeneration process and reduce environmental impacts, but system scale-up has been a challenge. Related CCS technologies have been explored to capture much more dilute CO2 from the atmosphere, either in combination with biomass combustion/energy production, bioelectrochemical carbon capture and storage (BECCS) or using base solvent absorption or solid sorbent adsorption. Generally, these are even more energy intensive and costly than point-source CO2 mitigation. However, a variety of potentially cheaper and high capacity air CO2 removal strategies have been proposed. For example, algae were used in bioelectrochemical systems to capture CO2 discharged from the anode in a microbial carbon capture cell, and recent studies found that the acids normally produced in the anolyte during the electrolysis of saline water can be reacted with carbonate or silicate minerals to generate strongly alkaline, CO2-absorptive solutions. This in effect greatly accelerates mineral weathering. When powered by non-fossil energy, the system is strongly CO2-emissions negative. However, the process is energy consumptive, with non-optimized, experimental systems using 426 to 481 kJ per mole of CO2 consumed and stored. When seawater or saline ground water is used, the geographic location of the operation is limited, and toxic Cl2 and halogenated organic compounds can be generated during electrolysis, posing environmental and health risks.
Despite the progress, most current CO2 capture studies have been conducted on either pure or highly concentrated CO2, which inherently limits the technology to CO2 generated from point sources such as power plants or refineries. It also limits the applicability of CO2 capture to new emissions without tackling the over 1,000 Giga tons of cumulative anthropogenic CO2 emissions since 1970, which has already posed great threat to the climate. It is estimated that even if 90% of CO2 emitted from 90% of the point sources is captured, 50% of the total anthropogenic CO2 emission will still be unaccounted for. This stresses the importance of ambient CO2 capture in meeting the grand carbon management goals. Currently, feasible ambient CO2 capture technologies are hampered by the high energy requirements of the process, and the lack of safe carbon storage options.
There is a need in the art for novel inexpensive and safe methods of capturing carbon dioxide. Additionally, there is a need in the art for novel methods of wastewater treatment and processing, especially methods that are able to transform and capture latent chemical energy contained within the wastewater. The present invention addresses these unmet needs.